In this study, compound-specific hydrogen isotope values of n-alkanes (n-alkane delta D) in a sediment core that dates to 18.5 cal ka BP were used to reconstruct the paleohydrological processes that couple glacial meltwater and precipitation at Lake Pumoyum Co, on the southern Tibetan Plateau. The lowest lake level, from 18.5 to 15.0 cal ka BP, may reflect both less glacial meltwater and less precipitation entering the lake. Glacial meltwater generally increased from 15.0 to 7.2 cal ka BP and decreased after 7.2 cal ka BP, whereas precipitation generally increased from 15.0 to 10.2 cal ka BP, decreased from 10.2 to 7.2 cal ka BP, then remained stable and moderate to the present. Comparisons of our results with records in adjacent areas and beyond suggest that the glacial meltwater supply during the past 15 cal ka corresponds well with changes in the Indian Summer Monsoon (ISM), which are driven by summer insolation at millennial time scales, whereas the precipitation does not match well with ISM changes during the Holocene. Therefore, paleohydrological processes at Lake Pumoyum Co have shown complex responses to climate change. Overall, our results emphasize that reconstruction of paleohydrological processes of lakes on the Tibetan Plateau should be carried out with caution because of glacial meltwater input.